High energy fuels



Oct. 9, 1962 R. A. FRANZ ETAL 3,057,705

HIGH ENERGY FUELS Filed June 22, 1959 GAS GAS u STRAIGHT RUN GASOLINE 8l2 CRUDE OIL CHARGE STOCK CATALYTiC 9 I 7 CRACKING CYCLE on.

LUBE STOCK SLURRY on. FLUX OIL l4 6 HIGH ENERGY FUEL AROMATIC |6DESULFUR- |8 HYDROGEN- 20 EXTRACTION IZATION ATION INVENTOR? RAYMOND A.FRANZ EO J. LANE ATTORNEY United States Patent 3,057,705 HIGH ENERGYFUELS Raymond A. Franz and Leo J. Spillane, El Dorado, Arie, assignorsto Monsanto Chemical Company, St. Louis, Mo., a corporation of DelawareFiled June 22, 1959, Ser. No. 822,114 2 Claims. (Cl. 44-80) Thisinvention relates to improved high energy fuels and in particular tofuels suitable for use in turbojet and turboprop engines.

One object of this invention is to provide a hydrocarbon fuel havingsubstantially increased energy content per unit volume over hydrocarbonfuels of the prior art.

Another object of this invention is to provide a hydrocarbon fuel forjet engines having a heat of combustion of from 125,000 B.t.u.s to160,000 B.t.u.s per gallon.

Another object of this invention is to provide a hydrocarbon fuel forjet engines having a heat of combustion in excess of 18,000 B.t.u.s perpound.

An additional object of this invention is to provide hydrocarbon fuelsfor jet engines utilizing hydrocarbon streams obtained in conventionalrefinery operations.

A particular object of this invention is to provide a hydrocarbon fuelfor jet engines having a heat of combustion of from 125,000 B.t.u.s to160,000 B.t.u.s per gallon and an extremely low pour point.

Additional objects will become apparent from the description of thisinvention.

Present jet fuels have a heat of combustion of only about 112,000B.t.u.s per gallon. They are prepared from petroleum hydrocarbons in thenaphtha and kerosene boiling range and accordingly consist largely ofparafiinic hydrocarbons. Present jet fuels also have a relatively highpour point which significantly limits their applicability.

It has now been found that a mixture comprising a major portion of thehydrogenated desulfurized aromatic extract of slurry oil and a minorportion of 3-isopropylbicyclohexyl, 4-isopropylbicyclohexyl or mixturesthereof, is an extremely useful high energy fuel characterized by anexceptionally high heat of combustion and an extremely low pour point.The following examples illustrate the novel compositions of thisinvention:

Example I A mixture was prepared comprising 90% by weight of thehydrogenated desulfurized aromatic extract of slurry oil and by weightof a mixture of the 3-isopropylbicyclohexyl and 4-isopropylbicyclohexyl.The hydrogenated desulfurized aromatic extract of slurry oil had aninitial pour point of F. The mixture prepared as described in thisexample had a pour point of F.

Example II A mixture was prepared comprising 80% by weight of thehydrogenated desulfurized aromatic extract of slurry oil and 20% byweight of a mixture of the 3-isopropylbicyclohexyl and4-isopropylbicyclohexyl. The hydrogenated desulfurized aromatic extractof slurry oil had a pour point of 15 F., while the mixture prepared asdescribed herein had a pour point of F.

Example III A mixture was prepared comprising 70% by weight of thehydrogenated desulfurized aromatic extract of slurry oil and by weightof a mixture of the I i-isopropylbicyclohexyl and4-isopropylbicyclohexyl. The hydrogenated desulfurized aromatic extractof slurry oil had a pour point of 15 F. while the pour point of themixture prepared as described herein had a pour point of 45 F. Thehydrogenated desulfurized aromatic extract of slurry oil had a heat ofcombustion of 18,493 B.t.u.s per pound and 136,-

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441 B.t.u.s per gallon, a specific gravity at 20/4 C. of 0.887 and an nof 1.4837. The mixture prepared as described in this example had a heatof combustion of 18,400 B.t.u.s per pound and 136,800 B.t.u.s pergallon, a specific gravity at 20/4 C. of 0.8917 and an n of 1.4821.

While the preceding examples have illustrated the use of mixtures of3-isopropylbicyclohexyl and 4-isopropylbicyclohexyl, similar results areobtained using either of the isomers alone. All proportions of mixturesof these isomers produce superior results in the practice of thisinvention.

The high energy fuels of this invention are composed of a majorproportion of the hydrogenated desulfurized aromatic extract of slurryoil and a minor proportion of 3-isopropylbicyclohexyl,4-isopropylbicyclohexyl or mixtures thereof. Particularly useful highenergy fuel compositions are obtained using from about 5% to about 45%by weight of total composition of the specified isopropylbicyclohexylisomers, and those compositions containing from about 15% to about 40%by weight of total composition of 3-isopropylbicyclohexyl,4-isopropylbicyclohexyl or mixtures thereof, are particularly preferred.

The isopropylbicyclohexyls as utilized in the present invention arepreferably made by the alkylation of biphenyl with propylene, such as bythe use of aluminum chloride as the alkylation catalyst. The alkylatedintermediate is then hydrogenated in order to obtainisopropylbicyclohexyl. The product thus obtained is composed almostexclusively of the 3- and 4-isomers which are used in preparing thenovel high energy fuels of this invention. These two isomers may beseparated if desired, but are equally useful when employed as a mixturein any proportion of the two isomers.

The utility of the hydrogenated desulfurized aromatic extract of slurryoil per se as a high energy fuel is disclosed and claimed in copendingapplication Serial No. 817,848, filed June 3, 1959. Its method ofpreparation is illustrated in FIGURE 1 which represents a schematic flowdiagram of a process for preparing the hydrogenated desulfurizedaromatic extract of slurry oil.

In the drawing, crude oil is introduced via line 1 into topping column2. In this column gas is taken overhead 3, straight run gasoline isremoved from an upper portion 4 of the column, lube oil stock is removedfrom the bottom portion 5 of the column, and flux oils are removed asbottoms 6 from the column. A 300 C.600 C. charge stock is removed vialine 7 from an intermediate section of the column and introduced into acatalytic cracker 8. The cracked products from the catalytic cracker arefed via line 9 into column 10 where gas is removed overhead 11, gasolineremoved via line 12 from the upper portion of the column, cycle oils, a200300 C. cut, are removed from the bottom portion of the column vialine 13 and slurry oil, boiling above 300 C., is removed as columnbottoms via line 14. This slurry oil generally contains about equalportions of paraffins and aromatics.

According to the process of this invention, this slurry oil is thenintroduced into an aromatic extraction system 15 where the aromatics areremoved from the slurry oil by extraction. The overall recovery of theparaffin layer from the slurry oil in a furfural extraction amounted to45.3% of the charge. Recovery of the aromatic oil amounted to 59.2% ofthe charge. The extraction was carried out in two stages, using twovolumes of oil for each volume of furfural. The aromatic-furfural layerwas separated and the furfural removed by distillation.

The aromatic extract of theslurry oil is then fed via line 16 to thedesulfurization unit 17. In this unit, the aromatic extract isdesulfurized. In a particular run the aromatic extract of slurry oilcontaining 4.72% sulfur was desulfurized with hydrogen over a cobaltmolybdenum sulfide catalyst. An average reaction temperature of 395 C.was maintained and an average reaction pressure of 1,200 p.s.i.g. wasmaintained. The sulfur content of the desulfurized material was reducedto 0.07%.

In order that the subsequent hydrogenation reaction can be carried outin a manner conducive of the greatest possible hydrogenation catalystlife, it is advisable that the sulfur content of the aromatic extract ofslurry oil be reduced to substantially zero. This at times may requireextraordinary desulfurization techniques. For example, in a particularrun it was found that the desulfurized aromatic extract of slurry oil asabove described containing 0.07% sulfur could be treated with metallicsodium at 230 C. to effect complete removal of the sulfur stillremaining. This significantly increased the catalyst life in thehydrogenation step.

The desulfurized aromatic extract of slurry oil is then fed via line 18to hydrogenation system 19 wherein the material is completelyhydrogenated. In a particular example, the desulfurized aromatic extractof slurry oil was hydrogenated over Raney nickel at a temperature in therange of from about 360 C. to 380 C. and a hydrogen pressure ofapproximately 2000 p.s.i.g. Substantially complete conversion of thearomatics to naphthenes was realized.

The hydrogenated desulfurized aromatic extract of slurry oil is thenintroduced via line 20 into fractionating column 21 where approximately90% of the product is taken overhead as high energy fuel andapproximately 10% of the product discarded as bottoms.

In a typical operation, a high energy fuel was obtained having a heat ofcombustion of 18,493 B.t.u.s per pound and 136,441 B.t.u.s per gallonand a pour point of l F. The material had a specific gravity at 20/4 C.of 0.887 and a n of 1.4837.

Conventional catalytic hydrocarbon cracking operations, well known tothose skilled in the art, can be used to prepare the heavy hydrocarbonoil streams from which the aromatics are extracted, desulfurized andthen hydro genated to produce high energy hydrocarbon fuels of thisinvention. Silica and alumina are conventional catalysts which can beemployed in the cracking step and these catalysts may be either naturalor synthetic. The catalyst can be employed as a fixed bed, as afluidized solid or as a moving bed, all of which are techniques wellknown to those skilled in the art. Any of the conventional feeds can beused in the catalytic cracking operation. Such feeds are usuallypetroleum oils containing a substantial portion boiling above 300 C.Heavy distillates boiling from 300600 C. or topped or reduced crude oilsare typical feed materials. Temperatures in the range of from about 425C. to about 500 C. are generally employed in the cracking step. Crackingpressures are generally relatively low, varying between atmospheric and7S p.s.i.g. Most cracking operations generally employed are of theregenerative type wherein the catalyst is periodically regenerated byburning with an oxygen containing gas. The cracking operation can becarried out in a once through system in which there is no recycle andonly fresh feed is charged to the unit, or a portion of the effluent canbe separated therefrom by fractional distillation and returned asrecycle to the feed stream to the catalytic cracker.

The products of the catalytic cracking zone or reaction are thenfractionated into several fractions including a distillate fractionboiling between about 200 C. and 300 C. which is commonly called cycleoil and a bottoms fraction boiling above 300 C. which is generallyreferred to as slurry oil.

In preparing the high energy hydrocarbon fuels of this invention theslurry oil i dearomatized to remove therefrom aromatic hydrocarbons.This dearomatization can be carried out by any technique well known inthe art but is most conveniently carried out by a solvent extraction.The manner in which this solvent extraction is carried out is notcritical. Any of the known solvents suitable for this purpose can beemployed to secure the desired aromatic extract. Furfural, liquid sulfurdioxide, mixtures of phenol and water, and the like are all suitable.The treatment is preferably carried out by countercurrent contact in aseries of extraction stages. Furfural is particularly suited for thispurpose since it can be used at relatively moderate temperatures and atmoderate solvent ratios. If desired, the extraction can also be carriedout through the use of solid adsorbent materials useful for thispurpose.

The equipment and procedure utilized for carrying out the aromaticextraction is not a critical limitation of this invention. A variety ofequipment can be employed.

The aromatic extract of slurry oil can be desulfurized by any of thetechniques well known to those skilled in the art. Cobalt molybdenumsulfide, tungsten nickel sulfide, nickel sulfide, and so forth, are allsuitable catalysts useful in the practice of this process.Desulfurization can be carried out at pressures ranging from p.s.i.g. upto 2000 p.s.i.g. or even higher if desired in particular circumstances.The desulfurization temperature can be varied from room temperature upto 500 C. or higher if desired. Any of the desulfurization equipmentwell known to those skilled in the art can be employed in this step ofthe process.

Any of the conventional techniques can be used to bydrogenate thedesulfurized aromatic extract of slurry oil in accordance with theprocess of this invention. Raney nickel, palladium, platinum, etc., areall catalysts useful in this hydrogenation step. Hydrogenation pressurescan be varied from 400 to 3000 p.s.i.g. or even higher if desireddepending upon the particular catalyst utilized. Hydrogenationtemperatures can be varied from room tem perature to 500 C. or higher,again depending upon the particular catalyst employed. Any of theconventional hydrogenation equipment with which those in the art arevery familiar can be used in the practice of this step of the process.

The hydrogenated desulfurized aromatic extract of slurry oil thusobtained can be used as such as a high energy fuel. It has been found,however, that the pour point of the material can be significantlylowered if the high boiler present in the material are discarded. Thiscan be accomplished by simple fractionation discarding up to 15% byweight of the bottoms.

The fuels of the instant invention are eminently suitable for use in jetengines, particularly turbojet and turboprop aircraft engines.

In the operation of turbojet engines, air is withdrawn from theatmosphere into an air compressor, compressed and delivered to thecombustion chamber of the engine where it is mixed with these fuels andthe mixture ignited. The resulting burning mixture of the fuel and airis diluted with secondary air and expanded through a turbine whichdrives the air compressor. In these engines, the hot mixture i expandedin the turbine in such a manner that only sufiicient energy is extractedfrom the gases to operate the compressor. The remaining energy isemployed to eject the gases in jet form through a jet pipe into theatmosphere and thereby produce thrust.

In using these fuels in turboprop engines, the operation is essentiallythe same except that the gases are almost completely expanded in theturbine, i.e., they are expanded almost down to the pressure of thesurrounding atmosphere, leaving only a relatively small amount of energyto produce thrust when ejected through the jet pipe. Thus, in turbopropengines, the majority of the energy from the hot expanding gases is usedto operate the compressor and the propeller and hence the thrust isobtained primarily from the latter.

In many turbojet and turboprop engines, only a single stage turbine isemployed. However, more than a single stage may be employed and, if so,guide vanes are introduced between each pair of turbine wheels. Afterleaving the last turbine wheel, the gas enters the jet pipe and isdischarged therefrom into the atmosphere.

The fuels of the instant invention may be used advantageously in thespark ignition piston-type aircraft engine, diesel engines, and turbineengines generally, but are particularly suitable for use in ramjet,turbojet and turbo prop aircraft engines. However, when the piston-typeand diesel engines are employed, the fuel/air ratios are adjusted so asto achieve substantially complete combustion of the air and fuel.

The fuels of the instant invention may be blended with other materialssuch as gasoline, kerosene, mixtures of gasoline and kerosene, otheraviation fuels, and with present hydrocarbon jet fuels to produce animproved fuel over the presently available fuel. More particularly, thefuels described herein may be added to the present aliphatic hydrocarbonjet fuels having a heat of combustion of about 112,000 B.t.u.s pergallon to raise the overall heat of combustion thereof. Moreover, thefuels described herein may be used in combination with fuel additives toobtain improved results as regards burning characteristics, etc.

The heat of combustion as given in this specification represents theheat of reaction between gaseous oxygen and liquid hydrocarbon toproduce gaseous carbon dioxide and water.

What is claimed is:

1. A high energy fuel consisting essentially of the hydrogenateddesulfurized aromatic extract of slurry oil, said slurry oil being thefraction boiling above 300 C. obtained in the catalytic cracking of aheavy petroleum distillate and from about 5% to about 45% by weight oftotal composition of an isopropylbicyclohexyl selected from the groupconsisting of 3-isopropylbicyclohexyl, 4- isopropylbicyclohexyl andmixtures thereof.

2. A high energy fuel consisting essentially of the hydrogenateddesulfurized aromatic extract of slurry oil, said slurry oil being thefraction boiling above 300 C. obtained in the catalytic cracking of aheavy petroleum distillate and from about 15% to about 40% by weight oftotal composition of an isopropylbicyclohexyl selected from the groupconsisting of 3-isop1'opylbicyclohexyl, 4- isopropylbicyclohexyl andmixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,749,225 Barnum et al June 5, 1956 2,765,617 Gluesenkamp et al Oct. 9,1956 2,911,352 Goretta et al. Nov. 3, 1959

1. A HIGH ENERGY FUEL CONSISTING ESSENTIALLY OF THE HYDROGENATEDDESULFURIZED AROMATIC EXTRACT OF SLURRY OIL, SAID SLURRY OIL BEING THEFRACTION BOILING ABOVE 300* C. OBTAINED IN THE CATALYTIC CRACKING OF AHEAVY PETROLEUM DISTILLATE AND FROM ABOUT 5% TO ABOUT 45% BY WEIGHT OFTOTAL COMPOSITION OF AN ISOPROPYLBICYCLOHEXYL SELECTED FROM THE GROUPCONSISTING OF 3-ISOPROPYLBICYCLOHEXYL, 4ISOPROPYLBICYCLOHEXYL ANDMIXTURES THEREOF.